Not a group Life Tap DoT, like some have thought, but is the upgrade to Vexing Mordinia...but the damge, to me, is worth the extra mana...1 Treant dead in PoN, and I have 65 - 70 mana left depending on resists...and I can lich down to under 50% health and get fully healed, unlike Vexing...this is a much better spell, and yes, for all those wondering, it stacks with EVERYTHING I have casted. =)
63 Warlock
Hallowed Pestilence
Quellious